Use of supported alkali metal hydride as catalyst for hydrodealkylation of aromatic hydrocarbons

Abstract

The application provides application of a supported alkali metal hydride as an aromatic hydrodealkylation reaction catalyst. The catalyst is low in cost, reusable, capable of catalyzing the cleavage of a carbon-carbon bond under mild conditions, realizing the hydrodealkylation reaction of an aromatic hydrocarbon, for example, is capable of realizing a conversion rate higher than 45% of the hydrodealkylation reaction of C8-C10 aromatic hydrocarbons at 200 DEG C-250 DEG C, greatly reducing the energy consumption of the reaction, and having high activity and high selectivity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of alkali metal hydride and light aromatic hydrocarbon, and particularly relates to application of a supported alkali metal hydride as a catalyst for aromatic hydrodealkylation reaction. BACKGROUND

[0002] Benzene, toluene, xylene (referred to as BTX, i.e. light aromatic hydrocarbon) is an important chemical substance for producing value-added products such as polymers, solvents, paints, polishing agents, and medicines. However, there is a huge imbalance between the supply and market demand of BTX. BTX is mainly derived from catalytic reforming of naphtha, extraction of cracking gas, and C9 + Aromatic hydrodealkylation reaction. Among them, BTX obtained by aromatic hydrodealkylation reaction is increasingly valued, especially as large-scale aromatic hydrocarbon processes are increasingly put into production, the production of aromatic hydrocarbon will be greatly improved, providing abundant aromatic hydrocarbon resources for this method. However, aromatic hydrodealkylation reaction usually requires a relatively high operating temperature of about 700-900℃, and the high energy consumption of this reaction leads to high process cost. Therefore, how to reduce the reaction temperature of this process and reduce the energy consumption in the reaction process has become one of the key problems for efficient development of aromatic hydrodealkylation for preparing BTX and other high-value chemicals.

[0003] Compared with non-catalytic hydrodealkylation method, the method for preparing BTX by catalytic hydrodealkylation reaction has the advantages of low hydrogen consumption, high conversion rate and high selectivity. Therefore, it is crucial to develop a catalyst with high activity, high stability and low price under relatively mild conditions for reducing the energy consumption and cost of this process. With the extensive attention of researchers to the catalytic hydrodealkylation technology, various commercial processes such as TAC9, ZEOLYST / SK, Detol, etc. have also been developed. For example, in the Houdry Detol process, a heterogeneous catalyst containing chromium or molybdenum oxide, or a supported platinum catalyst (such as Pt / SiO2, Pt / Al2O3) is used to prepare benzene by reacting toluene and hydrogen, and the reaction temperature is usually 480-590℃ and the pressure range is 40-60 bar. Since the hydrodealkylation process is exothermic, the reaction can also be carried out at a lower temperature, but the catalyst is often deactivated at a low temperature. In addition, in most catalysts, noble metals such as Pt, Re and Pd are used as active components, which undoubtedly increases the production cost. In addition, many studied substrates are single model aromatic compounds such as toluene, rather than heavy aromatic compounds containing more C8-C10 components, which also limits the application of hydrodealkylation catalysts. SUMMARY

[0004] Based on the above technical status, the inventors have found, through a large number of experimental explorations, that a supported alkali metal hydride can be used as a catalyst for aromatic hydrodealkylation reaction and has high catalytic activity and stability under mild conditions.

[0005] The alkali metal hydride in the supported alkali metal hydride is supported on a carrier.

[0006] The carrier includes carbon materials, two-dimensional materials, oxides, etc. The carbon materials are not limited and include one or more of graphene, carbon nanotubes, nanodiamonds, etc.; the two-dimensional materials are not limited and include one or more of hexagonal boron nitride, graphite phase carbon nitride (g-C3N4), two-dimensional transition metal carbides / nitrides (i.e., two-dimensional transition metal carbides, nitrides or carbonitrides, denoted as MXene), etc.; and the oxides are not limited and include one or more of magnesium oxide, silicon oxide, rare earth oxides, etc.

[0007] The alkali metal hydride is not limited and includes one or more of lithium hydride (LiH), sodium hydride (NaH), potassium hydride (KH), rubidium hydride (RbH), cesium hydride (CsH), etc.

[0008] In the supported alkali metal hydride, the mass percentage of the alkali metal hydride is preferably 1% to 50%, and more preferably 10% to 50%.

[0009] In the supported alkali metal hydride, the mass percentage of the carrier is preferably 50% to 99%, and more preferably 50% to 90%.

[0010] When the supported alkali metal hydride is used as a catalyst for aromatic hydrodealkylation reaction, the active ingredient of the catalyst is the alkali metal hydride.

[0011] The preparation method of the supported alkali metal hydride is not limited and can be prepared by the following method:

[0012] The alkali metal and the carrier are mixed in a high-pressure reaction kettle, H2 is pressurized to 1 bar to 100 bar, and heated to 100°C to 300°C for reaction.

[0013] As a preference, the carrier is first calcined in nitrogen. The calcination temperature is preferably 200°C to 1200°C.

[0014] The aromatic hydrocarbons are not limited in the aromatic hydrocarbons hydrodealkylation reaction, and preferably are C8-C10 aromatic hydrocarbons, such as one or a mixture of several of o-xylene, m-xylene, p-xylene, mesitylene, o-ethylbenzene, n-propylbenzene, isopropylbenzene, ethylmethylbenzene, m-ethylmethylbenzene, n-propylmethylbenzene, isopropylmethylbenzene, p-isopropylmethylbenzene, naphthalene, tetrahydronaphthalene, dimethylethylbenzene, o-tertramethylbenzene, m-tertramethylbenzene, p-tertramethylbenzene, 1-methylpropylbenzene, butylbenzene, diethylbenzene.

[0015] The aromatic hydrocarbons hydrodealkylation reaction is carried out in a high-pressure reactor, the substrate aromatic hydrocarbons and the catalyst are added to the high-pressure reactor, a certain volume of solvent is added, and the aromatic hydrocarbons undergo dealkylation under the conditions of H2 pressurization and a certain reaction temperature to obtain a reaction product. The solvent is not limited, and includes one or a mixture of several of n-octane, n-pentane, n-hexane, etc.

[0016] The reaction product is toluene, benzene, and other reaction products, which vary depending on the substrate. Taking mesitylene as an example, the continuous hydrodealkylation reaction process is as follows:

[0017]

[0018] The aromatic hydrocarbons reactants and reaction products in the aromatic hydrocarbons hydrodealkylation reaction are subjected to online qualitative and quantitative analysis by using a gas chromatograph-mass spectrometer (GC-MS), and the conversion rate of the aromatic hydrocarbons hydrodealkylation reaction and the yield of each reaction product are obtained, which are defined as follows:

[0019] Conversion rate = (number of moles of reacted substrate / initial number of moles of substrate) x 100%

[0020] Yield of a certain reaction product = (number of moles of the reaction product generated / initial number of moles of substrate) x 100%

[0021] In the present application, the conversion rate of the aromatic hydrocarbons hydrodealkylation reaction and / or the yield of the reaction product can be adjusted by adjusting one or several of H2 pressure, reaction temperature, reaction time, mass percentage content of the alkali metal hydride in the supported alkali metal hydride, and molar ratio of the supported alkali metal hydride to aromatic hydrocarbons.

[0022] As a preference, the H2 is pressurized to 1 bar-80 bar.

[0023] As a preference, the reaction temperature is 150℃-300℃, and further preferably 200℃-250℃.

[0024] As a preference, the reaction time is 1h-20h.

[0025] Preferably, the molar ratio of the alkali metal hydride to the aromatic hydrocarbon in the catalyst is 1:100-1:1, and more preferably 1:10-1:1.

[0026] In the present application, the aromatic hydrocarbon is an aromatic hydrocarbon.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] (1) The present application discloses that the supported alkali metal hydride can be used as a catalyst for the hydrodealkylation of aromatic hydrocarbons. Due to the strong electron-donating ability of the alkali metal hydride, a free radical anion intermediate is generated by the single electron transfer from the alkali metal (Li, Na, K, Rb, Cs, etc.) to the unoccupied anti-bonding p-pπ* orbital of the aromatic hydrocarbon molecule. The free radical can play a role in the reaction with aromatic compounds and initiate a free radical chain reaction. Moreover, the catalyst can catalyze the cleavage of carbon-carbon bonds under relatively mild conditions, and the high abundance and low price of the alkali metal are conducive to reducing the preparation cost of the catalyst.

[0029] (2) The present application can adjust the conversion rate of the hydrodealkylation of aromatic hydrocarbons and / or the yield of the reaction product by adjusting one or more of the H2 pressure, the reaction temperature, the reaction time, the mass percentage of the alkali metal hydride in the supported alkali metal hydride, and the molar ratio of the supported alkali metal hydride to the aromatic hydrocarbon.

[0030] (3) The present application can realize the hydrodealkylation of various aromatic hydrocarbons at 150-250℃, and the conversion rate of the hydrodealkylation of C8-C10 aromatic hydrocarbons can be higher than 45%, even higher than 50%, at 200-250℃. The temperature is lower than the reaction temperature of the currently used industrial process, which greatly reduces the energy consumption and has high activity and selectivity.

[0031] (4) The supported alkali metal hydride as the catalyst for the hydrodealkylation of aromatic hydrocarbons can be recycled and reused without affecting the catalytic activity.

[0032] (5) When the supported alkali metal hydride is used as the catalyst for the hydrodealkylation of aromatic hydrocarbons, the active ingredient of the catalyst is the alkali metal hydride, and the carrier plays a high dispersion role. Both the alkali metal hydride and the carrier play an important role in the high activity of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Figure 1 is a schematic diagram of the hydrogenation reaction of SiO2 and sodium in a high-pressure reaction kettle in Example 1. DETAILED DESCRIPTION

[0034] The application will be further described in connection with the following examples. It needs to be pointed out that the following examples are intended to facilitate the understanding of the application, and non-essential improvements and adjustments made by those skilled in the art based on the content of the application still fall within the protection scope of the application.

[0035] The terms "comprising", "containing", and similar terms are to be interpreted as encompassing rather than exclusive or exhaustive meaning; that is, as "including but not limited to".

[0036] Example 1:

[0037] The mass percentage of NaH in the silica-supported sodium hydride (NaH / SiO2) is 30%, denoted as 30wt.% NaH / SiO2. The 30wt.% NaH / SiO2 is prepared by a melt impregnation method as follows:

[0038] Take 210mg SiO2 carrier, pretreat it by calcination at 550℃ for 6h under N2 flow of 30mL / min, and then use it as the carrier. Take 90mg of sodium alkali, mix it with the carrier, and then place it in a high-pressure reactor for 10h of hydrogenation reaction at 110℃ and 10bar H2, as shown in Figure 1 After the reaction, wait for it to cool to room temperature, and then discharge the remaining gas to obtain 30wt.% NaH / SiO2.

[0039] Use the prepared 30wt.% NaH / SiO2 as the catalyst to perform catalytic o-xylene hydrodealkylation in a high-pressure reactor as follows:

[0040] Put o-xylene and 30wt.% NaH / SiO2 into a high-pressure reactor, with a molar ratio of NaH to o-xylene of 1:1, add n-octane, and react at 80bar H2 and 250℃ for 20h.

[0041] Example 2:

[0042] The preparation method of 30wt.% NaH / SiO2 is the same as that in Example 1.

[0043] Use the prepared 30wt.% NaH / SiO2 as the catalyst to perform catalytic m-xylene hydrodealkylation in a high-pressure reactor as follows:

[0044] Put m-xylene and 30wt.% NaH / SiO2 into a high-pressure reactor, with a molar ratio of NaH to m-xylene of 1:1, add n-octane, and react at 80bar H2 and 250℃ for 20h.

[0045] Example 3:

[0046] 30 wt. % NaH / SiO2was prepared in the same way as in Example 1.

[0047] The prepared 30 wt. % NaH / SiO2was used as catalyst to carry out catalytic xylene hydrodealkylation in a high-pressure reactor, in particular as follows:

[0048] Xylene and 30 wt. % NaH / SiO2were put into a high-pressure reactor, the molar ratio of NaH to xylene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2and 250°C for 20 h.

[0049] Example 4:

[0050] 30 wt. % NaH / SiO2was prepared in the same way as in Example 1.

[0051] The prepared 30 wt. % NaH / SiO2was used as catalyst to carry out catalytic ethylbenzene hydrodealkylation in a high-pressure reactor, in particular as follows:

[0052] Ethylbenzene and 30 wt. % NaH / SiO2were put into a high-pressure reactor, the molar ratio of NaH to ethylbenzene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2and 250°C for 20 h.

[0053] Example 5:

[0054] 30 wt. % NaH / SiO2was prepared in the same way as in Example 1.

[0055] The prepared 30 wt. % NaH / SiO2was used as catalyst to carry out catalytic mesitylene hydrodealkylation in a high-pressure reactor, in particular as follows:

[0056] Mesitylene and 30 wt. % NaH / SiO2were put into a high-pressure reactor, the molar ratio of NaH to mesitylene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2and 250°C for 20 h.

[0057] Example 6:

[0058] 30 wt. % NaH / SiO2was prepared in the same way as in Example 1.

[0059] The prepared 30 wt. % NaH / SiO2was used as catalyst to carry out catalytic cumene hydrodealkylation in a high-pressure reactor, in particular as follows:

[0060] Cumene and 30 wt. % NaH / SiO2were put into a high-pressure reactor, the molar ratio of NaH to cumene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2and 250°C for 20 h.

[0061] Example 7:

[0062] The 30wt.% NaH / Si02was prepared in the same way as in Example 1.

[0063] The prepared 30wt.% NaH / Si02was used as catalyst to catalyze the hydrodealkylation of m-ethyltoluene in a high-pressure reactor, in particular as follows:

[0064] The m-ethyltoluene and 30wt.% NaH / Si02were put into a high-pressure reactor, the molar ratio of NaH to m-ethyltoluene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2and 250°C for 20h.

[0065] Example 8:

[0066] The 30wt.% NaH / Si02was prepared in the same way as in Example 1.

[0067] The prepared 30wt.% NaH / Si02was used as catalyst to catalyze the hydrodealkylation of p-isopropyltoluene in a high-pressure reactor, in particular as follows:

[0068] The p-isopropyltoluene and 30wt.% NaH / Si02were put into a high-pressure reactor, the molar ratio of NaH to p-isopropyltoluene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2and 250°C for 20h.

[0069] Example 9:

[0070] The 30wt.% NaH / Si02was prepared in the same way as in Example 1.

[0071] The prepared 30wt.% NaH / Si02was used as catalyst to catalyze the hydrodealkylation of naphthalene in a high-pressure reactor, in particular as follows:

[0072] The naphthalene and 30wt.% NaH / Si02were put into a high-pressure reactor, the molar ratio of NaH to naphthalene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2and 250°C for 20h.

[0073] Example 10:

[0074] The 30wt.% NaH / Si02was prepared in the same way as in Example 1.

[0075] The prepared 30wt.% NaH / Si02was used as catalyst to catalyze the simultaneous hydrodealkylation of a mixture of o-xylene, m-xylene, p-xylene and mesitylene in a high-pressure reactor, in particular as follows:

[0076] o-xylene, m-xylene, p-xylene and mesitylene and 30 wt.% NaH / SiO2 were put into a high-pressure reactor, the molar ratio of NaH, o-xylene, m-xylene, p-xylene and mesitylene (NaH:o-xylene:m-xylene:p-xylene:mesitylene) = 4:1:1:1:1, n-octane was added, and the reaction was carried out at 80 bar H2 and 250°C for 20 h.

[0077] Comparative Example 1:

[0078] The preparation method of 30 wt.% NaH / SiO2 was the same as that in Example 1.

[0079] The prepared 30 wt.% NaH / SiO2 was used as a catalyst to carry out catalytic naphthalene hydrodealkylation in a high-pressure reactor, specifically as follows:

[0080] Naphthalene and 30 wt.% NaH / SiO2 were put into a high-pressure reactor, the molar ratio of NaH to naphthalene was 1:1, n-octane was added, and the reaction was carried out at 10 bar H2 and 250°C for 20 h.

[0081] Comparative Example 2:

[0082] The preparation method of 30 wt.% NaH / SiO2 was the same as that in Example 1.

[0083] The prepared 30 wt.% NaH / SiO2 was used as a catalyst to carry out catalytic tetrahydronaphthalene hydrodealkylation in a high-pressure reactor, specifically as follows:

[0084] Tetrahydronaphthalene and 30 wt.% NaH / SiO2 were put into a high-pressure reactor, the molar ratio of NaH to tetrahydronaphthalene was 1:1, n-octane was added, and the reaction was carried out at 10 bar H2 and 250°C for 20 h.

[0085] Comparative Example 3:

[0086] The preparation method of 30 wt.% NaH / SiO2 was the same as that in Example 1.

[0087] The prepared 30 wt.% NaH / SiO2 was used as a catalyst to carry out catalytic tetrahydronaphthalene hydrodealkylation in a high-pressure reactor, specifically as follows:

[0088] Tetrahydronaphthalene and 30 wt.% NaH / SiO2 were put into a high-pressure reactor, the molar ratio of NaH to tetrahydronaphthalene was 1:1, n-octane was added, and the reaction was carried out at 5 bar H2 and 250°C for 20 h.

[0089] Comparative Example 4:

[0090] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0091] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0092] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0093] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0094] Comparative Example 5:

[0095] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0096] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0097] Comparative Example 6:

[0098] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0099] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0100] Comparative Example 7:

[0101] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0102] The 30wt.% Na / SiO2was prepared by a melt impregnation method as follows:

[0103] (1) Put o-xylene and 30 wt.% NaH / SiO2 into a high-pressure reactor, the molar ratio of NaH to o-xylene is 1:1, add n-octane, and react at 80 bar H2and 250 °C for 20 h;

[0104] (2) The 30 wt.% NaH / SiO2 after reaction is recycled to catalyze o-xylene hydrodealkylation reaction, that is, the same volume of o-xylene is added into the high-pressure reactor to catalyze o-xylene hydrodealkylation reaction, and the reaction is carried out at 80 bar H2and 250 °C for 20 h.

[0105] Comparative Example 8:

[0106] The 50 wt.% NaH / SiO2 is prepared by a melt impregnation method as follows:

[0107] Take 150 mg of SiO2 carrier, and pretreat the carrier by calcining at 550 °C under N2 flow of 30 mL / min for 6 h. Take 150 mg of sodium base, mix with the carrier, and then place in a high-pressure reactor to carry out hydrogenation reaction at 110 °C and 10 bar H2for 10 h, as shown in the following formula: Figure 1 After reaction, the reaction system is cooled to room temperature, and the remaining gas is discharged to obtain 50 wt.% NaH / SiO2.

[0108] The prepared 50 wt.% NaH / SiO2 is used as a catalyst to carry out catalytic o-xylene hydrodealkylation reaction in a high-pressure reactor as follows:

[0109] Put o-xylene and 50 wt.% NaH / SiO2 into a high-pressure reactor, the molar ratio of NaH to o-xylene is 1:1, add n-octane, and react at 80 bar H2and 250 °C for 20 h.

[0110] Comparative Example 9:

[0111] The 30 wt.% NaH / SiO2 is prepared by the same method as in Example 1.

[0112] The prepared 30 wt.% NaH / SiO2 is used as a catalyst to carry out catalytic o-xylene hydrodealkylation reaction in a high-pressure reactor as follows:

[0113] Put o-xylene and 30 wt.% NaH / SiO2 into a high-pressure reactor, the molar ratio of NaH to o-xylene is 1:10, add n-octane, and react at 80 bar H2and 250 °C for 20 h.

[0114] Comparative Example 10:

[0115] The 30 wt.% NaH / SiO2 is prepared by the same method as in Example 1.

[0116] The prepared 30wt.% NaH / SiO2 was used as catalyst to carry out catalytic o-xylene hydrodealkylation reaction in a high-pressure reactor, specifically as follows:

[0117] The o-xylene and 30wt.% NaH / SiO2 were put into a high-pressure reactor, the molar ratio of NaH to o-xylene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2 and 150°C for 20h.

[0118] Comparative Example 11:

[0119] The 30wt.% NaH / SiO2 was prepared by the same method as Example 1.

[0120] The prepared 30wt.% NaH / SiO2 was used as catalyst to carry out catalytic o-xylene hydrodealkylation reaction in a high-pressure reactor, specifically as follows:

[0121] The o-xylene and 30wt.% NaH / SiO2 were put into a high-pressure reactor, the molar ratio of NaH to o-xylene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2 and 250°C for 10h.

[0122] Comparative Example 12:

[0123] The 30wt.% KH / SiO2 was prepared by a melt impregnation method, specifically as follows:

[0124] The SiO2 carrier was weighed at 210mg, pretreated by calcination at a temperature of 550°C under N2 gas at a flow rate of 30mL / min for 6h, and then used as a carrier. The alkali metal potassium was weighed at 90mg, mixed with the carrier, and then placed in a high-pressure reactor to carry out a 10h hydrogenation reaction at 110°C and 10bar H2. After the reaction, the remaining gas was discharged after cooling to room temperature, and 30wt.% KH / SiO2 was obtained.

[0125] The prepared 30wt.% KH / SiO2 was used as catalyst to carry out catalytic o-xylene hydrodealkylation reaction in a high-pressure reactor, specifically as follows:

[0126] The o-xylene and 30wt.% KH / SiO2 were put into a high-pressure reactor, the molar ratio of KH to o-xylene was 1:1, n-octane was added, and the reaction was carried out at 80 bar H2 and 250°C for 20h.

[0127] Comparative Example 13:

[0128] The 30wt.% NaH / MXene was prepared by a melt impregnation method, specifically as follows:

[0129] Take 210 mg MXene carrier, pretreat it by calcining in N2 at 30 mL / min and 550℃ for 6h, then use it as the carrier. Take 90 mg of sodium alkali, mix it with the carrier, and then place it in a high-pressure reactor for 10h of hydrogenation reaction at 110℃ and 10 bar H2. After the reaction, cool it to room temperature, and discharge the remaining gas to obtain 30 wt.% NaH / MXene.

[0130] Use the prepared 30 wt.% NaH / MXene as a catalyst to perform catalytic o-xylene hydrodealkylation in a high-pressure reactor, as follows:

[0131] Put o-xylene and 30 wt.% NaH / MXene into a high-pressure reactor, with a molar ratio of NaH to o-xylene of 1:1, add n-octane, and react at 80 bar H2 and 250℃ for 20h.

[0132] Use gas chromatography-mass spectrometry (GC-MS) to perform online qualitative and quantitative analysis of the aromatic hydrocarbon reactants and reaction products in Examples 1-10 and Comparative Examples 1-13, and the conversion and yield are shown in Table 1 below.

[0133] Table 1: Aromatic hydrocarbon conversion and yield in Examples 1-10 and Comparative Examples 1-13

[0134]

[0135]

[0136]

[0137] Note: Product 1 is the main reaction product in addition to toluene and benzene, and varies depending on the substrate.

[0138] From Table 1, we can conclude that:

[0139] (1) The catalyst 30 wt.% NaH / SiO2 has good catalytic activity for the hydrodealkylation of different C8-C10 aromatic hydrocarbons under mild catalytic conditions;

[0140] For example, in Examples 1-10, the conversion rate under the condition of 250℃ and 80 bar H2 for 20h is above 45%, and the conversion rate of other aromatic hydrocarbons is above 50% except for cumene, and the conversion rate of mesitylene and naphthalene is above 90%, and the conversion rate of naphthalene is even 100%.

[0141] (2) Other reaction conditions are the same, when the H2 pressure is reduced, the conversion of aromatic hydrocarbon dealkylation will be reduced, but the selectivity of dealkylation product will be improved, so it is also very important to determine the appropriate H2 pressure range in the hydrodealkylation reaction;

[0142] For example, in Comparative Example 2 and Comparative Example 3, when the H2 pressure is reduced, the conversion of aromatic hydrocarbon dealkylation will be reduced, but the selectivity of dealkylation product will be improved. The same rule can also be obtained by comparing Example 9 with Comparative Example 1.

[0143] (3) When the supported alkali metal hydride is used as the catalyst, both the alkali metal hydride and the carrier play an important role in the high activity of the catalyst;

[0144] For example, compared with the NaH / SiO2 catalyst in Example 1, the Na / SiO2 catalyst in Comparative Example 4 is used to catalyze the hydrodealkylation of o-xylene, and the activity test result shows that the yield of product 2 (toluene) is reduced by about 20 times.

[0145] Compared with the NaH / SiO2 catalyst in Example 1, the NaH catalyst in Comparative Example 5 is used to catalyze the hydrodealkylation of o-xylene, and the activity test result shows that the yield of product 2 (toluene) is reduced by about 20 times.

[0146] (4) As can be seen from Comparative Example 7, the supported alkali metal hydride used as the catalyst for the hydrodealkylation of aromatic hydrocarbons can be recovered and recycled after the reaction and does not affect the catalytic activity, and the yield of the dealkylation product is not significantly reduced.

[0147] (5) In Example 7, the intermediate ethyltoluene and in Example 8, the para-isopropyltoluene are mainly obtained by hydrodealkylation under the catalysis of NaH / SiO2, respectively, indicating that under the catalysis of NaH / SiO2, methyl is more easily hydrodealkylated than ethyl or isopropyl, which is due to the increase of the "steric effect" of ethyl and isopropyl relative to methyl.

[0148] (6) As can be seen by comparing Example 1 with Comparative Example 8, under the same other conditions, adjusting the mass percentage of alkali metal hydride can adjust the conversion and yield;

[0149] As can be seen by comparing Example 1 with Comparative Example 9, under the same other conditions, adjusting the molar ratio of the supported alkali metal hydride to the aromatic hydrocarbon can adjust the conversion and yield;

[0150] As can be seen by comparing Example 1 with Comparative Example 10 and Comparative Example 11, under the same other conditions, adjusting the reaction temperature or the reaction time can adjust the conversion and yield.

[0151] The above-described embodiments of the present application have been described in detail, and it should be understood that the above-described embodiments are only specific embodiments of the present application, and are not intended to limit the present application. Any modification, supplement or similar substitution within the principle range of the present application should be included in the protection scope of the present application.

Claims

1. Application of supported alkali metal hydrides as catalysts for the hydrodealkylation of C8-C10 aromatics; In the supported alkali metal hydride, the alkali metal hydride is supported on a support, which is silicon dioxide; The aromatic hydrocarbon is one or a mixture of several of o-xylene, m-xylene, mesitylene, m-ethyltoluene, and p-isopropyltoluene; The reaction temperature is 200°C. o C-250 o The conversion rate of C, C8-C10 aromatics hydrodealkylation reaction is higher than 45%.

2. The application as described in claim 1, characterized in that: The alkali metal hydrides include one or more of lithium hydride, sodium hydride, potassium hydride, rubidium hydride, and cesium hydride.

3. The application as described in claim 1, characterized in that: In the supported alkali metal hydride, the mass percentage of the alkali metal hydride is 1%-50%, and the mass percentage of the support is 50%-99%.

4. The application as described in claim 1, characterized in that: The method for preparing the supported alkali metal hydride includes mixing an alkali metal and a support in a high-pressure reactor, and reacting the mixture under pressure of 1 bar to 100 bar with H2.

5. The application as described in claim 4, characterized in that: The carrier is first calcined in nitrogen.

6. The application as described in claim 5, characterized in that: The roasting temperature is 200°C-1200°C.

7. The application as described in claim 1, characterized in that: The substrate aromatic hydrocarbon and the catalyst were added to a high-pressure reactor, and a solvent was added. Under H2 pressure and a certain reaction temperature, the aromatic hydrocarbon underwent a dealkylation reaction to obtain the reaction product.

8. The application as described in claim 7, characterized in that: The solvent includes one or more of n-octane, n-pentane, and n-hexane.

9. The application as described in claim 7, characterized in that: The conversion rate and / or yield of the reaction products of the aromatic hydrodealkylation reaction can be adjusted by regulating one or more of the following: H2 pressure, reaction temperature, reaction time, the mass percentage of alkali metal hydride in the supported alkali metal hydride, and the molar ratio of the supported alkali metal hydride to the aromatic hydrocarbon.

10. The application as described in claim 7, characterized in that: H2 is pressurized to 1-80 bar.

11. The application as described in claim 7, characterized in that: The reaction time is 1h-20h.

12. The application as described in claim 7, characterized in that: The molar ratio of alkali metal hydride to aromatic hydrocarbon in the catalyst is 1:100-1:

1.

13. The application as described in claim 7, characterized in that: The molar ratio of alkali metal hydride to aromatic hydrocarbon in the catalyst is 1:10-1:

1.

14. The application as described in any one of claims 7 to 13, characterized in that: The conversion rate of C8-C10 aromatics hydrodealkylation reaction is higher than 50%.

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